The use of fastening elements, which have fastening areas at which the optical element is fastened, is known for the purposes of holding optical elements on a mount. The optical element can be fastened to the fastening elements with a joining agent, for example with an adhesive. In general, the optical element lies on the fastening elements in the region of the fastening areas in order to support the optical element at the outer edge; however, it is also possible for the fastening elements to have lateral fastening areas in order to laterally clamp the optical element and thus achieve fastening in this manner. By way of example, the fastening elements may be embodied in the way of webs or the like, which possibly bridge an interstice between the inner edge of the mount and the outer edge of the optical element.
When use is made of UV or EUV radiation, it is generally necessary to protect optically active surfaces of optical elements using purge gas flows, since contaminations of the optically active surfaces may lead to transmission losses and irreversible damage of the optical elements. Particularly when using radiation at wavelengths of less than approximately 200 nm, it is advantageous to use small purge gas flows or a small purge gas volume per unit time. This is so because a noble gas, e.g. argon, must in some cases be used as the purge gas for the used radiation because of the absorption lines resulting from the purge gas.
By way of example, for the purposes of producing purge gas flows along optical surfaces, WO 2015/090862 A1 discloses the practice of providing at least one gas nozzle for producing a gas flow in an EUV lithography system for the purposes of removing contaminating substances from an optical surface arranged in the EUV lithography system, said gas flow forming a gas eddy in the EUV lithography system. The gas flow may extend along an optical surface such that the gas eddies are guided along the optical surface.
US 2010/0195076 A1 discloses an optical membrane element for an optical device for lithography, said membrane element having at least one membrane layer and a mount, which at least partly surrounds the at least one membrane layer and on which at least part of the edge of the membrane layer is fastened. Provision is made for at least one tensioning element for clamping the membrane in an adjustable manner. The optical membrane element has a holder, in which the mount is received, and the tensioning element has a length-adjustable connecting element between the mount and the holder. The membrane layer may be fastened to the holder in a gas-tight manner such that no membrane-free space remains between the contact points of the fastening elements on the membrane and on the holder.